This invention relates to a concrete-filled steel bearing wall and a method of manufacture thereof which are applicable to construction of concrete-filled steel bearing wall structures used in the construction of, for example, facilities related to nuclear power generation. To be more precise, it relates to a concrete-filled steel bearing wall comprising a pair of steel plates which face each other and are arranged in parallel with each other at a given distance, and concrete filled between these steel plates; namely, a so-called SC (steel concrete) structure and a method of production thereof.
Reinforced concrete structures and steel framed reinforced concrete structures have been used in the construction field for a very long time.
However, fabrication involving concrete has to be done after such structures are assembled at a construction site from reinforced steel and steel framed reinforced steel structures. A problem here is that the time period required for construction tends to be long. To cope with this problem, so-called SC structures which use composite structures of steel plates and concrete are widely used.
To put it simply, these structures include pairs of steel plates facing each other and linked with connecting members, such as steel web plates and steel rods, the spaces between the steel plates are filled with concrete, and a plurality of stud bolts are planted on the facing sides of the steel plates, so as to prevent a relative displacement between the steel plates and the concrete.
Since the construction of such structures which includes the assembly of steel plates or the like and concrete filling and other operations, could be done at plants equipped with facilities for these operations, it has become possible to greatly reduce the number of work days that has to be spent at construction sites and that tends to increase depending on weather conditions and other factors.
The walls used in these SC structures have conventionally been assembled according to the following procedures.
In a first such method shown in FIGS. 1(a) and 1(b), connecting members 1 having a length which is equal to the thickness of the concrete-filled steel bearing wall are connected by direct welding or by a similar method to one surface steel plate of a pair of surface steel plates 2, 2'. In a second method shown in FIGS. 2(a) and 2(b), connecting members 1' and 1" whose length is about a half of the thickness of the concrete-filled steel bearing wall are erected on the opposing surfaces of two surface plates 2, 2'. Then the connecting members 1' and 1" are joined using a splice plate 3 and bolts 4. According to a third method shown in FIGS. 3(a) and 3(b), one end of a connecting member 1"' which is slightly longer than the thickness of the concrete-filled steel bearing wall is formed into a screw thread, and the connecting member 1 is joined in advance at the other end to the surface of the steel plate 2' by welding or a similar method, so that the screw thread portion of the connecting member penetrates through an opening in the surface plate 2, and then the steel structure is assembled by fastening nut 5 to the screw thread and tightening the structure.
Then, irrespective of which method is used, the space between the two facing surfaces 2 and 2' is filled with concrete.
In FIGS. 1(a) to 3(b), numeral 6 indicates stud bolts 6 which are in advance planted to the facing surfaces of the steel plates 2 and 2'.
Although it is possible to use the thus produced concrete-filled steel bearing walls simply as walls, it is more effective to use them as composite structural members which also function as load-bearing members, such as pillars and supporting frames, in RC (reinforced concrete) structures and SFRC (steel framed reinforced concrete) structures. In this case, a large compression or shearing load is exerted on the wall surfaces. It is well known to those skilled in the art that concrete is weak against tensile forces, while it is strong against compression forces and bears compression loads.
Since concrete-filled steel bearing walls have a composite structure, the steel plates also bear the compression and shearing loads. A concrete-filled steel bearing wall is designed so that, of these two kinds of load, the shearing load is borne only by the steel plates. In any case, it is necessary to prevent the buckling of the above mentioned steel plates. Also, since the transfer of force in the space between the filled concrete and the surface of the steel plate occurs primarily through the stud bolts 6, the arrangement of these stud bolts is very important in dealing with the buckling of the surface steel plate.
In other words, stud bolts 6 fixed onto the surface steel plates 2 and 2' of the concrete-filled steel bearing walls are arranged in a square arrangement (FIGS. 4 and 5) in longitudinal and transverse directions according to conventional art. The most dominant forces which act on this type of structure are seismic forces. In a schematic drawing shown as FIG. 8, the hatched wall W receives a compressive force when the seismic force is in a direction perpendicular to the wall W, i.e, the x-axis direction, and it receives a shearing force when the seismic force occurs in the y-axis direction, which is parallel to the wall. In view of these forces, the intervals between the stud bolts are determined so as not to allow compression buckling or shear buckling to occur in the surface steel plates.
In such a conventional method as one shown in FIGS. 6 and 7, as indicated by hatching, the area B on the steel plate 2 which is surrounded by two rows of stud bolts 6 is regarded as an indefinitely long plate, and the intervals between the stud bolts 6 are determined so that the steel plate 2 does not buckle. With this design, because intervals between the stud bolts in the direction of main compression are made small so that the steel plate do not buckle with compression load, buckling due to shearing load does not occur as a matter of course.
Although the SC structures mentioned above were very effective in reducing time periods required for the construction of buildings, in order to broaden application areas and make them more practical, it is necessary to create a design that would greatly reduce the amount of materials used, make manufacture easier, simplify their structure, and increase their strength.
For example, according to conventional construction methods, the stud bolts are arranged in square (square arrangement), but since in this case there exits an imbalance between the compression buckling load and the shear buckling load, the strength against shearing is excessive.
In addition, the shearing load is borne basically by the surface plates, and their thickness is large. However, the characteristics of concrete material are not sufficiently utilized because the load supporting capacity of filled concrete may not be utilized.
In other words, it is necessary to realize a less expensive SC construction by letting the filled concrete bear some of the shearing load.
In order to provide a rationalized SC construction which would resolve the problems described above, it is necessary to improve the method of manufacture (manufacturing processes) of such structures.
According to conventional methods shown in FIGS. 1 and 2, a connecting member has to be welded to the inner surface of the opposing surface steel plate 2, 2' or connecting members 1 have to be connected with each other through splice plates 3. These manufacturing steps have to be carried out by a worker, and a sufficient space for this purpose is not available if the walls are thin.
Furthermore, a method which uses bolts and nuts, as shown in FIGS. 3(a) and 3(b), requires accurate positioning of openings required for bolts and accurate welding of the connecting members, so that high cost is unavoidable. Finally, since the nuts protrude out of the surface of the surface plate, not only is the appearance of the walls poor, but such an arrangement can also easily be an obstacle to mounting other in-building devices or equipment on the surface of the wall.